Traumatic lumbosacral instability: part 1 - proposing a definition and identifying underlying injury patterns

Abstract

Traumatic lumbosacral instability (TLSI) generally refers to a traumatic disruption of the lumbopelvic junction. The ambiguous use of this term has contributed to confusion and limited understanding of injuries that can impact lumbosacral stability. As of now, TLSI lacks a clear definition, and the underlying injury patterns remain inadequately characterized. Therefore, the objectives of the first part of this two-part series are: (1) to establish a precise definition of TLSI, (2) to identify and systematically characterize the injury patterns underlying TLSI, and (3) to outline principles for diagnosing and classifying these underlying conditions.

Keywords: Isler classification; Lumbopelvic instability; Lumbosacral dislocation; Lumbosacral dissociation; Lumbosacral facet; Lumbosacral joint; Pelvic ring; Pelvic ring fracture; Pelvic ring injury; Sacral fracture; Sacrum; Spinopelvic dissociation; Spinopelvic instability; Spondylopelvic instability; Transverse sacral fracture; Traumatic lumbosacral instability; Traumatic lumbosacral spondylolisthesis.

Fig. 1

Schematic illustration showing the specific sites of disruption associated with each of the four injury patterns resulting in TLSI: Lumbosacral dislocation injuries (LSDI; green), spinopelvic dissociation injuries (SPDI; red), unilateral vertical sacral fractures (UVSF) with ipsilateral L5/S1 facet joint involvement (yellow), and bilateral vertical sacral fractures without a transverse fracture component (BVSF; blue). SPDI is shown with U- and H-shaped variants, with dashed lines indicating distal fracture extensions of the H-shaped coronal fracture pattern. The right image shows a posterior view of the sacrum, displaying the UVSF proximal fracture line passing both through (*) and medial (**) to the S1 facet

Fig. 2

Classification of spinopelvic dissociation injuries (SPDI). Upper row: Classification according to Roy-Camille et al. [10], as modified by Lindahl et al. [13] (see text for detailed description). Lower row: Classification by fracture morphology in the coronal plane: U-, H-, Y- and lambda-shaped SPDI

Fig. 3

Unilateral vertical sacral fractures (UVSF) with ipsilateral L5/S1 facet joint involvement. Upper row: left: UVSF with the proximal fracture line passing lateral to the S1 facet do not affect lumbosacral stability; right: In contrast, UVSF with the proximal fracture line passing through (*) or medial to (**) the S1 facet have the potential to compromise lumbosacral stability, as first described by Isler. Lower row: Isler’s classification [64] of UVSF with the proximal fracture line passing either through or medial to, or both medial and lateral the ipsilateral S1 facet (see text for detailed description)